Document failure mode

From what I understand `failureMode=true` is what other clients call `failover=false` in the sense that if failure mode is on, the client does not failover to other servers but marks the failed server as dead until it come back up. This is confusing.

In the short term this should be documented. In the long term a configuration like `builder.setFailover(true)` could be added that sets `failureMode=false`.

@killme2008 If you don't mind I will submit a PR with some documentation.

Locate the existing configuration documentation for `failureMode` and related failover settings. Document how `failureMode=true` affects failover and server health, and clarify the relationship to other clients' `failover=false` behavior.

Written by the indexing model from the issue text.